In the PoE system defined in the IEEE standard, Power Sourcing Equipment (PSE) provides power to a Powered Device (PD) over a CAT-5 cable having two sets of twisted pairs. The first set includes two “signal” pairs of conductors, and the second set includes two “spare” pairs of conductors. PoE systems typically supply power from the PSE to the PD over one set of pairs in a CAT-5 cable—either the “signal” pairs or the “spare” pairs. Some higher power PoE systems provide power on all four pairs of conductors simultaneously.
For example, as shown in FIG. 1, the LTPoE++™ system provides power by tying the signal and spare pair center taps together. This system includes PSE circuitry 12 coupled to output circuitry composed of a signal pair power line 14, a spare pair power line 16, a signal pair return line 18 and a spare pair return line 20. The signal pair power line 14 is connected to the spare pair line 16, whereas the signal pair return line 18 is connected to the spare pair return line 20.
As illustrated in FIG. 2, each of the lines 14, 16, 18 and 20 is connected via the center tap of a respective Ethernet transformer to a respective pair of conductors in an Ethernet cable having four pairs of conductors—two signal pairs and two spare pairs. In particular, the signal pair power line 14 and the signal return line 18 are connected to the signal pairs 22 and 24 of the Ethernet cable, and the spare pair power line 16 and the spare pair return line 20 are connected the spare pairs 26 and 28 of the Ethernet cable. The Ethernet transformers connect the conductor pairs to the Ethernet PHY.
By contrast with the system in FIG. 1, the Cisco Universal Power over Ethernet (UPoE) system uses two PSE channels, one for the signal pairs and one for the spare pairs. As shown in FIG. 3, the UPoE system includes separate PSE circuitries 120 and 140. The PSE circuitry 120 provides power over the signal pair power line 14 and the signal pair return line 18, whereas the PSE circuitry 140 supplies power over the spare pair power line 16 and the spare pair return line 20. The spare pair return line 20 is connected to the signal pair return line 18.
These two techniques for high power delivery are not interoperable with each other if standard IEEE detection and classification schemes are used. Therefore, there is a need for a new technique that would provide interoperability among different high power PoE systems.